2 files changed, 79 insertions, 0 deletions

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 6bb7cf2de556..585b1a67cfbe 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -543,6 +543,82 @@ int __init of_flat_dt_match(unsigned long node, const char *const *compat)
         return of_fdt_match(initial_boot_params, node, compat);
 }
 
+struct fdt_scan_status {
+        const char *name;
+        int namelen;
+        int depth;
+        int found;
+        int (*iterator)(unsigned long node, const char *uname, int depth, void *data);
+        void *data;
+};
+
+/**
+ * fdt_scan_node_by_path - iterator for of_scan_flat_dt_by_path function
+ */
+static int __init fdt_scan_node_by_path(unsigned long node, const char *uname,
+                                        int depth, void *data)
+{
+        struct fdt_scan_status *st = data;
+
+        /*
+         * if scan at the requested fdt node has been completed,
+         * return -ENXIO to abort further scanning
+         */
+        if (depth <= st->depth)
+                return -ENXIO;
+
+        /* requested fdt node has been found, so call iterator function */
+        if (st->found)
+                return st->iterator(node, uname, depth, st->data);
+
+        /* check if scanning automata is entering next level of fdt nodes */
+        if (depth == st->depth + 1 &&
+            strncmp(st->name, uname, st->namelen) == 0 &&
+            uname[st->namelen] == 0) {
+                st->depth += 1;
+                if (st->name[st->namelen] == 0) {
+                        st->found = 1;
+                } else {
+                        const char *next = st->name + st->namelen + 1;
+                        st->name = next;
+                        st->namelen = strcspn(next, "/");
+                }
+                return 0;
+        }
+
+        /* scan next fdt node */
+        return 0;
+}
+
+/**
+ * of_scan_flat_dt_by_path - scan flattened tree blob and call callback on each
+ *                           child of the given path.
+ * @path: path to start searching for children
+ * @it: callback function
+ * @data: context data pointer
+ *
+ * This function is used to scan the flattened device-tree starting from the
+ * node given by path. It is used to extract information (like reserved
+ * memory), which is required on ealy boot before we can unflatten the tree.
+ */
+int __init of_scan_flat_dt_by_path(const char *path,
+        int (*it)(unsigned long node, const char *name, int depth, void *data),
+        void *data)
+{
+        struct fdt_scan_status st = {path, 0, -1, 0, it, data};
+        int ret = 0;
+
+        if (initial_boot_params)
+                ret = of_scan_flat_dt(fdt_scan_node_by_path, &st);
+
+        if (!st.found)
+                return -ENOENT;
+        else if (ret == -ENXIO) /* scan has been completed */
+                return 0;
+        else
+                return ret;
+}
+
 #ifdef CONFIG_BLK_DEV_INITRD
 /**
  * early_init_dt_check_for_initrd - Decode initrd location from flat tree
diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
index ed136ad698ce..19f26f8d2202 100644
--- a/include/linux/of_fdt.h
+++ b/include/linux/of_fdt.h
@@ -90,6 +90,9 @@ extern void *of_get_flat_dt_prop(unsigned long node, const char *name,
 extern int of_flat_dt_is_compatible(unsigned long node, const char *name);
 extern int of_flat_dt_match(unsigned long node, const char *const *matches);
 extern unsigned long of_get_flat_dt_root(void);
+extern int of_scan_flat_dt_by_path(const char *path,
+        int (*it)(unsigned long node, const char *name, int depth, void *data),
+        void *data);
 
 extern int early_init_dt_scan_chosen(unsigned long node, const char *uname,
                                      int depth, void *data);